It is known to construct a concrete tank using precast concrete panels which are cast on the site one on top of the other, these panels then being erected on a foundation with spaces being left between the panels. Using proper form boards, the spaces between the panels are then filled with concrete which is poured at the site. After the latter has cured, the forms are removed. Such tanks are then coated on one or both sides with material such as pneumatically placed mortar and are then stressed with wires wrapped under tension around the tank. See, for example, U.S. Pat. Nos. 3,280,525 and 3,408,784 issued respectively on Oct. 25, 1966 and Nov. 5, 1968.
However, the type of tank shown therein, and other known tanks, are relatively expensive in certain cases, in view of the additional steps involved in both the construction of the tank itself, and the necessity of transporting to the site the equipment for applying the pneumatically placed mortar.
In addition, when it is desired to pour concrete structures during severely cold weather, elaborate precautions must be taken to insulate the concrete against sudden changes in temperature. If, for example, the tanks described in U.S. Pat. Nos. 3,280,525 and 3,408,785 are wire wrapped in freezing weather, normally the entire wall area of the tank must be enclosed and heated to prevent frost from reaching the protective coating of pneumatic mortar. This entails a loss of time, of course, but more important, the cost of this protection makes it economically prohibitive, resulting in a shutdown of this work in the winter months of many sections of the country.
For more than thirty years, pneumatically placed mortar has been used as the exclusive material for protection of prestressing wire in wire wrapped tanks, despite the fact that its cost is high, the quality control is difficult and winter protection is prohibitively expensive.
There is a need, therefore, for a simple way of constructing and reinforcing concrete tanks which will be of higher quality and less expensive than those of the prior art, and which makes it economically feasible to build them during the winter months.